The present invention relates to a method of introducing a sample into a mass spectrometer or ion mobility spectrometer.
Low volatility analytes may be ionised from solution or by desorption at atmospheric pressure by techniques such as Electrospray ionisation (ESI), Atmospheric Pressure Chemical Ionisation (APCI), Atmospheric Pressure Matrix Assisted Laser Desorption Ionisation (AP-MALDI), Atmospheric Solids Analysis Probe (ASAP), Desorption Electrospray Ionisation (DESI) and Direct Analysis in Real Time (DART) etc. In order to mass analyse the resulting analyte ions, the ions must be introduced ions into a sub-ambient region of a mass spectrometer. An orifice is provided between the atmospheric pressure region in which the ions are ionised and the low pressure region of the mass spectrometer. In general, the larger the orifice is the more ions are passed into the mass spectrometer, for a given concentration of analyte. However, the larger the orifice is the greater the gas flow into the mass spectrometer. This is undesirable because expensive vacuum pumping equipment must be used in order to maintain the desired pressure within the mass spectrometer, particularly in the region of the analyser.
In contrast, sub-atmospheric pressure ionisation sources can be interfaced with the mass spectrometer without requiring pumping of such high gas loads from the vacuum chamber of the mass spectrometer. Examples of sub-atmospheric pressure ionisation sources include glow discharge, MALDI, electron impact, chemical ionisation and Matrix assisted inlet ionization ion sources. Introduction of low volatility sample material into these sources is typically achieved via a vacuum lock in which a sample stage is introduced into a separate chamber and this chamber partially evacuated before allowing the vacuum chamber of the mass spectrometer to be in fluid contact with this separate chamber. This avoids a large volume of gas entering the mass spectrometer. However, these vacuum locks are mechanically cumbersome, expensive and require additional rough pumping.
It is desired to provide an improved method of mass spectrometry or ion mobility spectrometry and an improved spectrometer.